Crystallization Process Of Glass Research Articles

Bi2O3 – GeO2 glass and transparent glass ceramic based on it

Glasses with the composition (in moles) 2Bi2O3, 3GeO2 have been obtained. They have different color and electric properties. This is due to the different concentration of bismuth ions with degree of oxidation different from +3. The characteristic temperatures of these glasses have been determined, and on the basis of these temperatures heat-treatment regimes were chosen in order to obtain a transparent glass ceramic. The effect of the glassmaking regimes on the glass crystallization process is established. Some physical–chemical properties of the glass ceramic obtained have been investigated.

Effect of Excess MgO Mole Ratio in a Stoichiometric Cordierite (2MgO·2Al2O3·5SiO2) Composition on the Phase Transformation and Crystallization Behavior of Magnesium Aluminum Silicate Phases

The effect of excess MgO, 2.0–4.0 mol ratios on the crystallization behavior and purity of μ-cordierite was investigated using X-ray diffraction (XRD), differential thermal analyzer, and TGA. Quantitative XRD, the Rietveld technique, was carried out using the HighScore Plus software. The glass crystallization process route was used with talc and kaolin as the main raw materials and compensated with MgO, Al2O3, and SiO2 accordingly. The crystallization temperature of the glasses decreased as a function of the MgO mole ratio. Less than 2.8 mol MgO increased the formation of α-cordierite up to 94 wt%. However, above 2.8 mol ratio, the forsterite phase started to appear, together with mullite, μ-cordierite, and spinel.

Electrical conduction in the vitreous and crystallized Li 2O–V 2O 5–P 2O 5 system

The glass-forming region of the Li 2O–V 2O 5–P 2O 5 system was examined. The glass transition temperature and stability of glass were enhanced with increasing P 2O 5 content. Li 2O–V 2O 5–P 2O 5 glasses show electronic or ionic conduction depending on the glass composition. The electronic conductivity increases with increasing V 2O 5 content, while the ionic conductivity is proportional to the Li 2O content. The effect of crystallization on the electrical conduction was also investigated. The ionic conductivity decreased by thermal crystallization. Drastic increase of electronic conduction was observed in the crystallization process in glasses of 50Li 2O–25V 2O 5–25P 2O 5 and its neighboring compositions. It was clarified that high electronic conduction occurs in a metastable crystalline phase prior to the thermal equilibrium crystallization.

Crystallization of μ-and α-cordierite in glass obtained via melting by concentrated radiant flux

The results of investigations of the influence of synthesis conditions on the crystallization behavior of cordierite glasses are presented. It is found that both ultraviolet radiation and the glass melting temperature influence the glass crystallization processes. The influence of small admixtures on the crystallization of μ-and α-cordierite is shown.

A novel ceramic material with medical application

Until now the basic methods used in manufacturing of wollastonite have been chemical (melting together with glass crystallization process, chemical coprecipitation) and sol - gel methods. A new and promising way of wollastonite fabrication is controlled pyrolysis of polysiloxane precursors with inorganic fillers. Heat treatment of such mixtures leads to the formation of wollastonite-containing ceramics already at about 1000?C. This is a relatively inexpensive and efficient method which enables to obtain complex shapes of the samples. The aim of this work was to obtain sintered, wollastonite-containing bioceramics and determine its bioactive features. Samples were sintered at three different temperatures: 1000, 1100 and 1200?C. Then the bioactivity of the wollastonite-containing ceramics was investigated by the ?in vitro? test in simulated body fluid. On the basis of the achieved results, it can be assumed that the obtained material possesses bioactive features.

Crystallization characteristics and physico-chemical properties of the glasses based on Li 2O–CaO–SiO 2 eutectic (954 °C) system containing magnesium oxide

The crystallization process of glasses in the Li 2O–CaO–SiO 2 (954 °C) eutectic system containing MgO at the expense of Li 2O and/or CaO were investigated by means of DTA, XRD, and SEM. Minor additives of CaF 2 or TiO 2 were added on the batch of the eutectic glass as nucleating agents. The relationship between the crystalline phases formed, heat-treatment applied and their effect on the properties were discussed. The crystallization of the glasses was greatly enhanced by modification processes, thus fine fibrous and prismatic-like growths were obtained therefrom. The dilatometric thermal expansion of the glasses and their corresponding glass-ceramics were determined. The thermal expansion properties of the glasses depend on the glass compositions. The addition of CaF 2 or TiO 2 as nucleating agent to the eutectic glass led to increase the α-values of the glasses. However, both the T g and T s values decreased. The α-values of the glasses were decreased with the increase of MgO at the expense of Li 2O and/or CaO, while both the transformation ( T g) and softening ( T s) temperatures increased. The thermal expansion coefficients of the crystalline materials exhibited a wide range depending upon the type and relative proportions of the crystalline phases formed. The chemical durability test, using acid solution, of the glass-ceramics was determined. The data obtained depend on the nature and concentration of crystalline phases present and microstructure.

Delayed nucleation in Fe 40Co 40P 14B 6 metallic glass

Metallic glass with a nominal composition of Fe 40Co 40P 14B 6 (numbers denote at.%) was prepared by the melt-spinning process. The as-quenched FeCo-based ribbons have good soft magnetic properties: the saturation magnetic polarization μ 0 M s=1.45 T, a quasistatic coercive force of 4 A m −1 and a maximum differential magnetic permeability of about 110 000 at 60 Hz. Fe 40Co 40P 14B 6 glass crystallizes by a eutectic reaction resulting in the face-centered cubic (f.c.c.) solid solution and the body-centered (b.c.) tetragonal (FeCo) 3(PB) compound. The crystallization temperatures, determined using differential scanning calorimetry, are approximately 60 K higher than those for Fe 40Ni 40P 14B 6. Kolmogorov–Johnson–Mehl–Avrami model has been modified to account for temperature dependencies of nucleation and crystal growth rates and has been employed to quantify the non-isothermal glass crystallization process. Two fitting parameters: the activation energy of atomic transfer across crystal/glass interface Q and crystal/glass interfacial tension σ, which govern crystal nucleation and growth, have been calculated from the set of experimental data of crystallization temperatures at different heating rates. While the estimated crystal growth rates in Fe 40Co 40P 14B 6 and Fe 40Ni 40P 14B 6 amorphous alloys are rather close, the homogeneous nucleation frequency in the FeCo-glass was found to be essentially lower than that in the FeNi-counterpart. It was concluded that a higher value of the crystal/glass interfacial tension σ is responsible for enhanced thermal stability of the Fe 40Co 40P 14B 6 glass.

Mössbauer analysis of crystallization processes in iron-soda-lime-silicate glasses

57Fe Mossbauer spectroscopy was used to observe the crystallization process in glasses with composition denoted by [0.50SiO2, 0.45Na2O, 0.05CaO]100-x(Fe2O3)x with x equal to 4, 10 and 16 mol%. It is shown that Mossbauer spectroscopy is a very suitable technique for detecting and checking the very early stages of crystallite formation in amorphous materials. The crystallization process was observed and qualitatively analysed by means of classical volume nucleation theory.

Glass-formation and crystallization kinetics

A review is presented of several aspects of crystallization processes in glass and their impact on glass-forming ability. Herein, both isothermal and non-isothermal processes are considered. For isothermal crystallization processes, generalizations of the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory are described and the status of certain features of nucleation rate and crystal growth calculations in glasses are given. For non-isothermal crystallization, some features of DTA/DSC analyses and critical cooling rate calculations for glass-formation are discussed, and generalizations of the standard theory for computation of the fraction crystallized are presented.

The thermal stability of chalcogenide glasses

Crystallization processes of GexS1-x (0.322≤x≤0.44) glasses have been studied by thermal analysis and a new simple method of kinetic analysis is proposed. This method allows the definition of an appropriate model characterizing the crystallization process of glass, as well as calculation of reliable kinetic parameters. Results of kinetic analysis allow definition of a thermal stability criterion which has a general applicability for any glass-forming system.

Glass formation and crystallization of liquid and glass rubidium: A constant-pressure molecular-dynamics study

Glass formation and crystallization processes in supercooled metallic liquid and the crystallization processes in glass are investigated for a rubidium system with 500 atoms by means of a constant-pressure molecular-dynamics technique. Calculations of thermodynamic and structural properties associated with the phase transitions are presented. The processes of structure transformation are analyzed by means of the atomic pair concepts, polyhedra, volume, energy, and pair distribution function. The results demonstrate a feature of structure transformation and show a clear picture of structure transitions during the cooling and heating processes. The glass formation has no sharp variations in the volume, the energy, or the structure, with temperature. However, the crystallization of both the supercooled liquid and the glass do have sharp variations. The results confirm that the transitions associated with these crystallization processes are first-order-like transitions, and that if there is a relaxation of the glass before the crystallization, the heating process which follows makes the glass more stable at low temperature. It is also confirmed that the cooling and heating rates have a strong effect on the transitions.

The kinetic analysis of the crystallization processes in glasses

The crystallization kinetics characterized under non-isothermal conditions using thermal analysis (TA) techniques are discussed. A simple and consistent method of kinetic analysis of TA data has been developed. The method allows one to perform the correct determination of the most suitable kinetic model and subsequent calculation of all kinetic parameters needed for a quantitative description of the studied process. This method was used to study the kinetics of crystallization of (GeS 2 0.3(Sb 2S 3) 0.7 glass measured by various DSC and DTA instruments. The influence of instrumental factors is discussed with respect to the reliability of the kinetic information deduced from the experimental data.

Crystallization of Li2O · Al2O3· 6SiO2 Glasses Containing Niobium Pentoxide as Nucleating Dopant

Niobium pentoxide (T form, orthorhombic system) was utilized to promote devitrification in Li2O · Al2O3· 6SiO2 glasses. Two or more mole percentage of this nucleating dopant enhanced crystallization in these glasses. Glasses containing 4.0 and 8.0 mol% T‐Nb2O5 exhibited a high tendency to form dispersed TT‐Nb2O5 (monoclinic system) precipitates during the glass quenching process. The crystallization process in glasses containing 2.0 or 4.0 mol% T‐Nb2O5 occurred as microphase separation, followed by the formation of dispersed TT‐Nb2O5 crystalline precipitates (760°C), followed by β‐quartz solid‐solution (ss) formation (850° to 900°C) heterogeneously nucleated from the precipitates. β‐quartz(ss) transformed to β‐spodumene(ss), along with a polymorphic transition from the TT‐Nb2O5 to M‐Nb2O5 (tetragonal system) crystalline phase.

Sol-gel synthesis, sintering and properties of a potassium-substituted cordierite

Cordierite (Mg2A14SisO18) and cordierite-based glassceramics are promising materials for electronic packaging due to both dielectric constant and thermal expansion being lower than the values for alumina [1-4]. Nevertheless, materials with good strength and high density together with improved dielecric characteristics are difficult to obtain using conventional methods (crystallization from glass or mixed oxide solid-state reaction) because of the very narrow sintering range of the stoichiometric compound. So, sintering of cordierite ceramics is generally done using additives such as titanium, alkali or alkaline-earth oxides [1, 5]. However, dense cordierite bodies have recently been obtained at low temperature using the sol-gel route [6, 7]. As we have already shown that a potassium-substituted cordierite, synthesized by using the glass crystallization process, presented a much lower thermal expansion coefficient than pure cordierite, it seemed of interest to check the ability to obtain dense ceramics of potassium cordierite using a sol-gel method [8, 9]. This letter deals with the elaboration and some characteristics of sol-gel-prepared K0.sMgzA14.sSi4.5Oi8 cordierite ceramics. In the silica-alumina system, the hydrolysiscondensation kinetics of the silica precursors, e.g. Si(OR)4, is strongly slower than that of the alumina alkoxides, AI(OR)3, and therefore leads generally to heterogeneous materials [10]. In order to avoid this difficulty we have used a method proposed by Yoldas [11], which consists in a partial hydrolysis of the silica precursor before introducing the alumina one. The starting materials used in this study were pure commercial silicon ethoxide (Si(OC2H5)4), aluminium butoxide (Al(OC4Hg)3), potassium acetate and magnesium nitrate. The processing flow chart is given in Fig. 1. The use of hydrazine (N2H4"H20) allows a rapid gelation (often less than 1 h) and the gels obtained are quite homogeneous and translucent. Drying the gels at 60°C always leads to a greyish powder containing a large amount of carbon (up to 13.9%) and hydrogen in a lesser extent (~3 .7%) (hydrogen, carbon and nitrogen by Carlo Erba 1106 analyser). This colour remains after the subsequent thermal treatments, thus indicating that carbon cannot be fully removed in this way. The gels were therefore washed with hydrogen peroxide H202 and dried at 60 ° C: residual amounts of both carbon and hydrogen decreased down to -~ 3%. Thermogravimetric analysis curves clearly show the influence of the

ESR and Mössbauer Studies of Crystallization Process of Iron Phosphate Glass

Abstract 0.7Fe2O3–0.3P2O5 glass was prepared by using a twin-roller method and the crystallization process of this glass was followed by means of ESR and Mössbauer spectroscopy in order to understand the state and the behavior of iron ions in the glass. The ESR line shape of the quenched 0.7Fe2O3–0.3P2O5 glass was much broader than that of the crystallized glass heat-treated at 710 °C for 5 h. Moreover, the linewidth of Mössbauer spectra decreased monotonously through the crystallization process. These facts indicated that there existed a distribution of ligand fields around iron ions in the glass. The Mössbauer parameters, that is the isomer shift and the quadrupole splitting, of the 0.7Fe2O3–0.3P2O5 glass showed that Fe3+ ions in this glass were laid on distorted octahedral ligand fields. The magnetic interaction working in the 0.7Fe2O3–0.3P2O5 glass at room temperature was dipole–dipole interaction. Besides, the Mössbauer spectrum of the glass exhibited no internal field line at room temperature. Hence, the glass is considered paramagnetic at room temperature. At the first stage of crystallization process, the α-Fe2O3 particles precipitated were sufficiently small and so the specimen was superparamagnetic, as revealed from the ESR and Mössbauer spectra of heat-treated specimens.

Dependence of crystallization rate on amorphous structure

Glass formation in melt quenching is possible only when the resistance to homogeneous crystal nucleation remains high as the melt is deeply undercooled through its labile regime to the glass temperature, which implies that the crystallization process in glass forming materials must be one in which the short range order is reconstructed. The constraints on glass structural models imposed by this reconstructive requirement will be discussed. If heterophase nucleants operate, crystallization may be suppressed during melt quenching if the activation energy for crystal growth is sufficiently high. The mechanisms of crystal growth in metals and in covalent network materials will be compared. Molten or glassy B 2O 3 under atmosphere pressure does not crystallize at a measurable rate even when seeded, but does readily crystallize at pressures exceeding 7 to 10 kilobars. An explanation, which may have more general applicability, will be offered for this B 2O 3 crystallization “anomaly”.

The role of titania and titania mixtures in the nucleation and crystallization of spodumene—willemite—diopside glasses

The nucleation and crystallization processes in glasses and melts of different compositions within the system spodumene—willemite—diopside, using different proportions of TiO 2 and mixtures of TiO 2+ZrO 2 and TiO 2+ZrO 2+F as nucleating agents, have been studied by employing a combination of DTA, X-ray diffraction, and optical and scanning electron microscopy. Incorporation of titania or its mixtures in the base composition modified the crystallization kinetics, as expressed by variations observed on the peak temperatures and spans of the DTA exotherms of crystallization. These nucleants also influenced the type and relative proportions of the crystallized phases, transformation temperatures, degree of metastability of β-Zn 2SiO 4 and β-eucryptite ss 1 1 ss=solid solution; β-eucryptite ss was also named β-quartz ss in the literature. , and the texture of the resultant glass-ceramic. TiO 2 additions lowered the onset crystallization temperatures and favoured the crystallizability. TiO 2 catalyzed the pyroxene and β-eucryptite ss formation and also the transformation of the latter into β-spodumene ss. TiO 2+ZrO 2 mixtures enhanced the crystallization but retarded phase transformation. Addition of F to TiO 2+ZrO 2 showed a synergistic effect to the action of TiO 2 and also greatly facilitated willemite formation. The proposed nucleation mechanism of titania and its mixtures involves the enhancement of liquid-liquid phase separation followed by the separation of a zinc titanate phase which heterogeneously nucleates the crystallization of the glass bulk.

Kinetic study of crystallization of glass by differential thermal analysis—criterion on application of Kissinger plot

For the purpose of analyzing the crystallization process of glass by DTA, the modified Kissinger-type equation was derived on the basis of the nucleation and growth equations, and the validity of the equation was ascertained by applying to the crystallization of Li 2O·2SiO 2 glass whose kinetic data regarding crystallization are already well-known. The modified Kissinger-type equation is identical with the so-called Kissinger equation only when the crystallization starts at the surface and grows towards the inside of the glass one-dimensionally. The conditions required for applying the Kissinger plot or modified Kissinger-type plot to the crystallization of glass were discussed, and it was concluded that the crystallization mechanism should be known in order to obtain the meaningful activation energy.

Kinetics of crystallization processes in glass forming melts

A survey is given of experimental results concerning the kinetics of nucleation and the mechanism of crystal growth in glass forming systems. The main aim of the review is, however, to correlate the kinetics of overall crystallization processes in glass forming melts with structural changes taking place in the initial melt during crystallization. Detailed investigations of the kinetics of overall crystallization summarized here for a number of phosphate and silicate melts, indicate that even in relatively simple glass forming melts crystallization is in fact connected with considerable molecular (e.g. anionic) reconstructions. It is shown that the kinetics of nucleation in glass forming melts can be described in terms of the more general, transient formulation of the classical theory of phase formation. Experimental evidence on the mode of crystal growth in glass forming melts is summarized, attention being concentrated on data obtained at low undercoolings. The conditions for the predominant manifestation of the basic mechanisms of crystal growth (normal, spiral and via surface nucleation) are considered, accounting for the structure of the initial melts and the state of the crystal/melt interface.

EPR of intermediate group ions in oxide glasses and products of their crystallization: Part I

The results of the EPR speotroscopic study of glasses and the products of their crystallization containing Cr3+ ion are given. Spectra were interpreted using the results of the study of a theoretical line form. Experiments show the advisability of the usage of Cr3+ EER in studies of the structural peculiarities of glassy media, because EPR spectra of this ion are extremely sensitive to the changes of composition and phase transitions during the crystallization processes in glasses.